Strain IV Armenian hamsters, Cricetulus migratorius (2n equals 22), progressively develop hemolytic anemia, autoimmune disease, and type B RCN, and corresponding erythro-, myelo-, and immuno-blastic crises. In vitro explants adapt as lymphoblastoid or immunoblastoid cell lines. In addition, symptomatic animals may develop associated hepatocarcinomas and pheochromocytomas. An overt synthesis of immunoglobulin accompanies disseminated tumor transplants in syngeneic recipients. Immunoblastoid cells feature one or more heteromorphic inverted tandem duplications involving at least one A-T rich Q-band. The duplicated DNA may correspond to visible loci implicated in the synthesis and/or the variability of immunoglobulins, as proposed by Smithies (1963). Marker chromosome analyses will be used to determine whether the 3 blastogenic crises represent progression of a single multipotent stem cell, or the sequential activation of 3 independent stem cell populations. Mutational studies with clonal isolates having altered patterns of inverted tandem duplications will assist in determining if these particular sites are implicated in the structural variability of the monoclonal gammopathies noted in parent tumor cell lines. Other parameters to be employed while assessing these specificities include the characteristic single cell "clonal" growth of individual lymph node tumors, and possible acquisition if immunocompetency (serum reactivity against nuclear antigen), associated with delayed gut- associated lymphadenopathy.